Under what General Services Administrator Jay Solomon calls the "living buildings program," federal building could become shopping malls.

You may someday be able to have dinner outdoors on the plaza, buy a hat in the lobby and then see a play in the auditorium of a federal office building.

For some time, private developers have been multi-use projects that combine elements such as apartments, office space, shopping areas and movie theaters. The idea is to make better use of the space and for longer periods of time - especially at night and on weekends.

GSA, which operates the government's public buildings, is going to start opening up the buildings for multiple use.

Under the Public Buildings Cooperative Use Act of 1976, the agency was directed to encourage the location of commercial, cultural, educational and recreational facilities and activities in public buildings.

The old Post Office Building on Pennyslvania Avenue here will be the first government building to be opened for commercial use under the new legislation. Space is to be made available for shops and restaurants and additional uses will be planned for the building after it is restored and modernized.

The old Post Ofiice in St. Louis is to be similarly redeveloped and vitalized.

GSA has also been authorized to make auditoriums, meeting rooms, courtyards, rooftops and lobbies of gaged in cultural, educational recreational activities will be able to rent space as long as the operation of the buildings is not disrupted.

Space on major pedestrian access levels, courtyards and rooftops of public buildings can also be leased for commercial use. The rent will be at the prevailing commercial rate and leases may be negotiated without competitive bidding.

Just because the space is available doesn't mean people will flock to a building at night. The use will still have to be imaginative and inviting enough to lure people out of their homes - and away from suburban shopping centers.